There are many conventional types of levels, including bubble type and pendulum type. A bubble type level includes a container cup partially filled with liquid. When the bubble type level is put on an inclined surface of a working desk, the liquid will flow to a lower place within the container due to gravity force. An inclined angle of the surface of the working desk can be measured by observing the liquid surface or movement of the bubble in the container. For example, U.S. Pat. No. 7,497,021 discloses a multi-axis bubble vial device, and U.S. Pat. No. 5,313,713 discloses an electronic level with display scale and audible tone scale.
An electrolyte level sensor has a plurality of electrically conductive particles or magnetic particles added in the liquid. An electrically conductive layer or a magnetic layer is coated or attached on an inner surface of the container. The movement of the liquid can be sensed as corresponding electrically conductive or magnetic positions. In this manner, the inclined angle can be obtained. For example, Brooks Automation Company (USA) owns U.S. Pat. No. 6,526,668 disclosing an electronic level and U.S. Pat. No. 4,932,132 disclosing an electronic level apparatus and method. The above mentioned two bubble type levels have single or dual axes inclined angles measuring functions. But they lack sufficient sensitivity, resolution and precision. Therefore, they can only be used as ordinary levels to measure large inclined angles.
The pendulum level works according to a principle that the pendulum is always perpendicular to the horizontal plane of earth. When the pendulum level is put on an inclined surface, the pendulum inside the device will swing a same inclined angle as that of the main body of the level. A non-contact displacement sensor for measuring the relative displacement of the pendulum relative to the sensor is disposed in the main body of the level, thus achieving the purpose of inclination measurement. If the level is installed with a high precision non-contact displacement sensor, such as a capacitive displacement sensor used to perform high sensitive, high resolution and high precision measurement, the level can be used as a high precision level for measuring small inclined angle. However, such a high precision level in market can only perform single axis measurement. Examples of such products include TALYVEL™ produced by Taylor Hobson Company of Britain and LEVELTRONIC™ produced by Wyler Company of Swiss.
The pendulum level can harness the optoelectronic sensing principle. Examples include the electronic level disclosed in U.S. Pat. No. 4,827,624 and the dual-axis optoelectronic level in TW patent M402416. The pendulum level can also harness the differential electrode sensing principle, as illustrated by the electronic level indicator disclosed in U.S. Pat. No. 5,027,522. The above mentioned pendulum levels all have pendulums immersed in liquid which provides damping effect for stopping vibration of the pendulums. Thus, they have more components.
Summarizing the art above, the bubble type level has fewer components but does not have high precision, and the pendulum type level has more components but only a part of them has high precision performance. The art would be advanced by an improved simple type dual axes level with high precision.